You might want to consider soda blasting them...are they already textured a bit?
I believe those are called "Keystone turbo's". The General Lee had them on the Dukes of Hazard.
Just the marks on the fins from the machining. They should smooth out fairly easy. Just talked to my neighbor who works with metals. He's going to take the worst one with him to work and give it a bath with some phosphate somethingororther and pressure wash em. He says they should clean up real good.